The present invention relates to self-locking fasteners and, in particular, to improvements therein for assuring uniform locking between the mating peripheries of the self-locking fastener and of the article into which the fastener is threaded, and further to use of such fasteners in relieving stresses in supporting reflective and other surfaces.
Conventional fasteners, such as self-locking screws, as exemplified in FIG. 1, are slotted to provide segments which, for screws are peripherally threaded. The fastener is first inserted or threaded into engagement with a mating surface or screw threads of an article. A bolt or other spreading object, placed within the self-locking fastener/screw, then forces the segment and its periphery and any threads therein into locking engagement with the surface/threads of the article, so that the fastener/screw no longer can rotate. Such an arrangement, as will be more fully described with respect to FIG. 1, provides a narrow annular locking contact of the segments with the article surface or threads. While acceptable in some applications, the lack of full locking contact is not acceptable for other applications, such as discussed below.
In addition, when such fasteners and screws are utilized as supports for precisely positioned optical elements such as reflective surfaces, the use of such screws or other conventionally used supports often results in optical distortions of plates supporting the reflective surfaces, excessive wear of the threads, and slippage of the locking engagement. In particular, when adjusting the optical alignment of such elements, three adjustment fasteners, which commonly comprise screws, are placed in a point support triangular pattern to enable one article to be tilted with respect to its support and, thereafter, to hold them in a locked position after adjustment of the tilt. When one point support is displaced from its original setting, the original plane is effectively rotated into a new plane, about an axis formed by the other two pivot points provided by the screws. Conversely, if all three points are constrained so as not to move, the plane will remain in that oriented position.
Such a plane may comprise the reflective surface of a mirror, which is mounted on a plate and held relative to another structure in an optical system. For alignment and retention of the mirror relative to the optical system, it is necessary to control the distances of the mirror surface as measured along the three perpendicular lines from the surface to the pivot points defined by the three adjustment screws. The environment of such an optical system often is not stable, being subject to jolts and bending motions exerted thereon, and can cause one or more screws to slip. Even a small slip may misalign the optical alignment of the system. Therefore, stability is only as good as the extent to which the adjustment screws do not creep after having been locked in place.
In addition, during the alignment operation, the plates are drawn together after their adjustment screws are turned to provide an initial spacing between the plate and its support, after which the initial locking engagement between mating threads fixes the spacing. The screws may need to be further adjusted slightly after a certain thread pressure has been achieved in the initial locking engagement and, in so doing, causes excessive abrasion and galling in the threads with possible lack of a solid metal-to-metal contact caused by debris which may also contaminate the optical system. Thus, the plates are held sufficiently tightly together to maintain accuracy of alignment, while the screws are released only to the extent necessary for readjustment. Because the locking between threads is essentially an annular contact comprising arcs, those portions of the screws at the annular point contact become distorted and/or galled.
A third problem also exists with use of three adjustment screws. During the adjustment, two screws are held in position while a third is adjusted so as to adjust the tilt of the reflective surface. As one screw moves with respect to the others to cause the tilting of the reflective surface and the plate into which the screws are threaded, the bolts which spreads the screws arcuately bend. Such bending may either damage the screws or, if the screws are sufficiently rigid in their locked positions, distort the plate and its reflective surface. The bending of the bolts also causes spring energy to be stored therein and, when the spring energy is released, the bolt will move or the threads will slip and will result in misaligning the prior adjustment.